The invention relates to a method and a device for protecting motor vehicles against theft, in particular a keyless, remote-controlled central locking system and an electronic immobilizer.
A known system for protecting against theft (DE 197 11 901 C1) divides the code signal generators assigned to the vehicle into what are referred to as external keys and internal keys. With external keys, the central locking system and the immobilizer can be remote-controlled. The internal keys are used only to activate the vehicle and are disabled if they are located in the vehicle and the user leaves the vehicle, and/or locks the doors of the vehicle, using another authorized key. The internal keys located in the vehicle are enabled again as soon as the doors are unlocked with an authorized key and/or the vehicle door is opened and an authorized key is recognized. Every internal key located in the vehicle is enabled as a result of each authorized access to the motor vehicle. A method for automatically enabling all the disabled code signal generators is disclosed.
Therefore, even keys which the user of the motor vehicle does not know are located in the interior of the motor vehicle are therefore enabled. Under unfavorable circumstances this can lead to a situation in which an unauthorized user can come into possession of an operationally capable key.